If you mean plastic, both about the same, Female adaptors with the bush leave slightly more room in the box, as opposed to the Male where the thread sometimes protrude into the box, both push on the conduit and if you want you can pvc glue them on, but not always necessary.
Generally water pump pliers tighten the bush or lockring but some do up enough just by hand.
A coupler is a device designed for joining two lengths of conduit together.
In steel conduit the design of the couplers means they can also be used in compbination with a bush to connect to a box. In plastic conduit couplers are different from adapters.
In PVC, always known them as conduit adapters. Female by far the most common in my experience, as leaves loads of room in back box and where conduit terminates into trunking etc.
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